There were many reasons for the failure of the second crusade. One of these was definitely the mistakes made by Louis VII but there were also other reasons that inffluenced the failure of the crusade. These included the lack of Byzantine aid by Manuel Commenus and also the rivalry between Kings.
Firstly, Byzantiu did play a part in the failure of the failure of the second crusade. One reason for this was that Manuel was more concerned with Byzantines position than the fate and position of the crusader states. Manuel saw the crusade as an inconvenience as it prevented him from his plans to attack Sicily, this resulted in him giving the crusade little acknowledgement. Another factor was that the Byzantium emperor had an understanding with the Turks as well as an alliance with the Sultan of Rum. All this would be under threat if he was to help the crusade so it made more sense to give the franks directions rather than supplies as this would anger the turks and could possibly start a war. Also, during the first crusade Baldwin and Bohemond refused to restore territory to the Byzantine emperor so this removed any interest he may have had in aiding the crusade. The pillaging Greek towns led to Manuel refusing to provide supplies top aid his troops alone. This then led to Christians fighting amongst each other which then led to a weaker overall Crusader force, which resulted in the crusade lacking man power and strength. The fact that 90% of troops were wiped out at Dorylaeum certainly had an impact on the failure of the crusade as this reduced the amount of troops on the crusade significantly. This was due to the lack of aid and ships from the Byzantine Emperor - Manuel, which then led to more troops having to travel by foot. As a result of this many troops were lost to disease as well as being sabotaged by the Turks. Overall the lack of aid from the Byzantine emperor resulted